1. Copyright Notice
This patent document contains information subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent, as it appears in the U.S. Patent and Trademark Office files or records but otherwise reserves all copyright rights whatsoever.
2. Field of the Invention
The present invention, in certain respects, relates to Internet Protocol telephony. In other respects, the present invention relates to a method of bridging Internet Protocol based voice calls.
3. Description of Background Information
Voice, fax and other forms of information have traditionally been carried over dedicated circuit-switched connections of a public switched telephone network (PSTN). Circuit-switched calls use pulse code modulation (PCM) to transmit analog data over the PSTN in digital form.
In order to make a voice call over an IP network, the PCM data of the PSTN has to be encoded to a packet form. One method that a user may use to communicate in a voice call over an IP network is to place a call over the PSTN. The PCM data would be encoded to one or more packets via a gateway device and sent over a packet switched network. A networked server would receive the packet encoded voice signals of the user from the gateway device. In this manner, a user may call a designated number to reach the networked server to receive voice mail messages. The user may decide to call the person who left the message while listening to the voice message. This could be accomplished by the user entering a special code; thus, causing the server to make a second call to the person who left the voice message. However, in order for the user on the first call and the user on the second call to communicate with each other, the server must bridge the two calls. To bridge the calls, the server decompresses the encoded voice signal from the first call user. The voice signal is converted back to PCM format and then switched over a time division multiplexing (TDM) bus that carries PCM data. The data from the TDM bus is then compressed and encoded back to packet form and transmitted over the network to the second call user. Similar to the actions used to transmit the voice signal of the first user call, the server must decompress the voice signal from the second call user. The decompressed voice signal of the second caller is switched over a TDM bus, and then encoded back into a packet form to be transmitted to the first caller.
Using this process to bridge voice calls, it is necessary to encode and decode the voice data twice for each IP call, which results in increased latency in the network. What is needed is an efficient and effective way to bridge voice stream data over a network with a minimum latency.